Field of the Invention
The present application relates generally to fabricating porous substrates and their use in sequencing DNA.
Description of the Related Art
DNA sequencing includes methods and technologies that can be used to determine the order of nucleotide bases—adenine, guanine, cytosine, and thymine—in a molecule of DNA. Various methods known in the art for sequencing portions of DNA molecules are known and include chain termination methods with fluorescent dies and gel electrophoresis. Membrane based methods for sequencing DNA that measure the blocking current are also known in the art. DNA molecules have been measured by constructing pores in a thin membrane and electrophoretically pulling that DNA through the pore. The synthesis of such pores has been accomplished by using biological systems that generate pores through lipid bilayers with structures similar to the pores found in cell membranes or by using inorganic materials, such as graphene or silicon nitride. Measurement of the DNA and identification of individual polymerases is generally accomplished by measuring the “blocking current”, which is the ion current that flows through the pores. The molecule can be held within the pore in a predictable way so that the shape and size can be determined through such blocking current. However, these methods have drawbacks such as slow measurement and noisy data. The data can have a lot of noise because the ion current is measured with a large series resistance using the electrolyte as the contact to the entrance and exit of the pore. The methods for measuring blocking current can also be inaccurate because the readings can depend on the orientation of the DNA strand as it passes through the pores. Also, multiple DNA strands can pass through the pore simultaneously and make the signal difficult to interpret for the desired strand of DNA.